The "for" in v.1 indicates that Paul is giving evidence for the struggle for their maturity he refers to in 1:28-29. He want them to know that even though he hasn't seen them face to face (vv. 1,5) he is devoted to their "full assurance" (v. 2) and to their "firmness of faith in Christ" (v. 5). To this end he continues to paint an irresistible picture of who Christ actually is. In Him are "hidden all the treasures of wisdom and knowledge" (v. 3).